Investigation Methods and Procedures - Geotechnical Engineering Investigation - page 62

FIGURE 2.35
Terrain conductivity meter (EM34). (Courtesy of Geonics.)

occasional ground collapse in the old mines. The area was surveyed using an EM34 and
the results identified an anomaly with 0 ( Figure 2.37) . Continuous airtrack probes and

core borings confirmed that the mine was at a depth of about 40 ft.

Ω

Ground-Probing Radar (GPR)
Applications
Ground-probing (ground-penetrating) radars are used as a rapid method of subsurface
profiling. They are designed to probe solids relatively opaque to radar waves, such as
pavement-reinforcing rods and bases, as well as subpavement voids, buried pipes,
bedrock surfaces and overlying boulders, caverns, tunnels, clay zones, faults, and ore bod-
ies. Images consist essentially of wavy lines. They are difficult to interpret and primarily
locate anomalies that require additional investigation.

Theoretical Basis
Energy is emitted in the radio portion of the electromagnetic spectrum ( Figure 2.4) ,
of which some portion is reflected back to the radar equipment. Various materials
have differing degrees of transparency to radar penetration. New GPRs are digital
with an improved signal-to-noise ratio using fiber optics cables and improved antenna
design.